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Algae and Climate Change
Susan S. Kilham
Department of Biodiversity, Earth & Environmental Science
Drexel University
Climate change is happening at
unprecedented rates
• Increasing CO2. Now more than 400 ppm
• Increasing ocean acidification
• Increasing temperatures, especially in the Arctic
• Sea level rise
• Stratification changes
• Increasing habitat loss
• Other anthropogenic changes (e.g., toxic chemicals)
My personal journey to awareness of climate impacts
• Early interest in affects of temperature on growth rates and nutrient
utilization of algae, especially diatoms (Mechling and Kilham. 1982. J.
Phycol. 18: 199-205; van Donk and Kilham. 1990. J. Phycol. 26: 40-50.)
• Natural phytoplankton community experiments along Si:P ratio
gradients at two temperatures showed communities dominated over a
wider range by diatoms at 9ᵒC and more by green algae at 15ᵒC (Tilman,
Kiesling, Sterner, Kilham, and Johnson. 1986. Arch. Hydrobiol.106: 473-485.)
• Research on phytoplankton in the large lakes of the Greater
Yellowstone Ecosystem (GYE) with Edward Theriot and Sebastian
Interlandi
Generalizations about major diatoms species in GYE
• Asterionella formosa: needs high Si, moderate N,
favored by early stratification and warm
epilimnion
• Aulacosira subarctica: low light specialist, favored
by deep mixing, low nutrients, early stratification
• Cyclotella bodanica: grows under low-N, usually
in late summer, favored by low precipitation years
Generalizations about major diatoms species in GYE
• Stephanodiscus minutulus: grows well under ice, best
competitor for Si, grow rapidly under high nutrients because of
small size
• Stephanodiscus yellowstonensis: grows best in drought years,
local maxima in metalimnion, better than S. niagarae under Nlimitation
• Stephanodiscus niagarae: needs moderate N & P, does better in
high precipitation years and grows well under low light (not in
Yellowstone L.)
• Fragilaria crotonensis: rare in Yellowstone Lake, requires high N,
moderate Si, good competitor for P (grows best in Lewis Lake
which is most P-limited
C:N, C:P, C:Si and N:P ratios
with depth during the
growing season in Lewis,
Jackson and Yellowstone lakes
4 potentially limiting resources:
N, P, Si, light
Sampled every week during the
growing season, every 5 m from
0 to 25 or 50m
Enumerated algae by biovolume
Interlandi, Kilham & Theriot, 1999. Limnol. Oceanogr. 44: 668-682
Abundance by biovolume of most abundant
diatoms over the growing season
The point of maximum abundance of each species
was distinct and varied according to the 4-part ratio
Interlandi, Kilham & Theriot, 1999. Limnol. Oceanogr. 44: 668-682
Diversity of planktonic algae
Threshold levels for limitation
0.85 x µmax for least efficient species
P: 0.32 µmol/L
N: 3.0 µmol/L
Si: 139 µmol/L
Light 150 W/m2
Interlandi & Kilham, 2001. Ecology 82:1270-1282
Impacts of El Niño in GYE
• Winter precipitation lower and therefore N-loading lower
(lower N:P)
• Total diatom biomass lower in Yellowstone and Jackson
lakes
• Si concentrations higher because of lower diatom
demand (higher Si:P)
• Predictable changes in phytoplankton community
structure because of changes in ratio gradients
Impacts of El Niño in GYE
• Early ice off and earlier stratification (higher Light:N)
• Shallower epilimnion (depends on early summer storm
activity)
• S. yellowstonensis historically favored during drought
periods
• A. formosa and S. minutulus favored by high Light:N in
early summer
• C. bodanica favored by increased N-limitation in summer
The Climate Challenge
• The magnitude of climate change
is remarkable: We have already
exceeded the maximum CO2
concentration. experienced in
the past 740,000 yrs. and will
soon exceed that experienced in
tens of millions of years.
The Climate Challenge
• The rates of abiotic change are unprecedented. The
rise in CO2 in the past 150 years is 100 to 1000 times
faster than at any point in the past 420,000 yrs. and
is still accelerating.
• These changes pose serious challenges to species
that must either acclimate, adapt, or go extinct.
The Impact of Temperature Rise on
Respiration and Heterotrophic Metabolism
Calculated using metabolic
models, a 4 ºC warming is
predicted to result in a 20%
increase in net primary
production, but a 43% increase
in oxygen consumption
Seagrass Meadows
The net effect is a decrease in biomass;
also true for agricultural crops
Harris, Nixon and Duarte, 2006. Estuaries and Coasts 29: 343–347
Major Algal Groups and Major Biological Processes in Selected Ocean Regions
NATL – North Atlantic; EPAC- Equatorial Pacific; ARC- Arctic; ANT- Antarctic; NPAC- North Pacific
Toseland et al. 2013. Nature Climate Change 3:979-984
Major Algal Groups and Major Biological Processes in Selected Ocean Regions
NATL – North Atlantic; EPAC- Equatorial Pacific; ARC- Arctic;
ANT- Antarctic; NPAC- North Pacific
Toseland et al. 2013. Nature Climate Change 3:979-984
T of eukaryotic
phytoplankton the density of
ribosomes to make protein. P
rich ribosomes in warmer
oceans will result in organism
N:P, N-demand. Changes in
phytoplankton stoichiometry
driven by T may play a critical
role in resource allocation and
biogeochemical cycling of major
nutrients.
Role of Metabolic Processes
• Sequenced eukaryotic phytoplankton metatranscriptones
• CCA analysis revealed that temperature accounts for
28.3% of metabolic variability, similar to nitrate (31.7%),
phosphate (34.9%), and light (30.2%).
• Translation of proteins was strongly affected by
temperature.
• The rate of protein synthesis in cells appears to at higher
temperature which is compensated by ribosome
density.
Toseland et al. 2013. Nature Climate Change 3:979-984
Role of Metabolic Processes
• Membrane associated processes involved in ion
transport, photosynthesis and respiration were
significantly in the EPAC metatranscriptones.
• Under low temperatures, cells invest more in
biosynthesis, whereas under high temperatures more
resources are invested in photosynthesis.
Toseland et al. 2013. Nature Climate Change 3:979-984
Balancing Physical and Metabolic Effects
Lewandowska et al. (2014) used 1500 L
mesocosms (2 temps; 6 nutrient flux
levels; Baltic Sea plankton) to explore the
physically mediated effect of warming on
stratification which indirectly affects
nutrient supply rates and direct effects
of warming on metabolic rates.
Lewandowska et al. 2014. Ecology Letters 17:614-623.
Balancing Physical and Metabolic Effects
As T :
-heterotrophic processes are more sensitive to T
than autotrophic ones.
– higher grazing rates by zooplankton
–lower phytoplankton biomass
-faster recycling by bacteria which could increase
phytoplankton productivity.
Lewandowska et al. 2014. Ecology Letters 17:614-623.
Balancing Physical and Metabolic Effects
In nutrient replete waters (a) T
influences plankton mainly through
metabolic changes.
Such systems are typically dominated
by large diatoms.
Warming creates a growing
imbalance between grazing and algal
growth which reduces algal biomass.
Lewandowska et al. 2014. Ecology Letters 17:614-623.
Balancing Physical and Metabolic Effects
In nutrient-limited waters (b) T
influences phytoplankton mainly
through physical mechanisms related
to stratification and nutrient supply.
Low nutrients favor small plankton
and copepods switch to eating larger
ciliates.
Lewandowska et al. 2014. Ecology Letters 17:614-623.
Changes in phytoplankton communities
•Climate affects phytoplankton directly
through physiology and indirectly through
water column stratification and grazing
(Winder and Sommer 2012. Hydrobiologia 698:5-16)
•Increasing T increases growth rates under
light saturating conditions
Changes in phytoplankton communities
• Vertical mixing is a key variable because
stratification affects light and nutrient availability
for growth. Smaller, buoyant species have an
advantage under reduced mixing.
• Warming increases consumption by herbivores
more strongly than primary production which
strengthens top down control (Sommer and Lewandowska 2011. Global
Change Bio. 17:154-162)
Dance of the Phytoplankton
• Climate change will impact the availability of growth-limiting
resources.
• The biomass of phytoplankton is not proportional to their division
rates.
February chlorophyll
February mixed layer depth
Feb depth integrated chl
Bloom climax chl concentration
Behrenfeld. 2014. Nature Climate Change. 4:880-892.
Dance of the Phytoplankton
• Physical processes can trigger blooms even while division rates are
decreasing. This is because changes in division rates are paralleled by
proportional changes in grazing, viral attack and other loss rates.
• This leads to a trophic dance between predators and prey which can
result in massive blooms.
• The blooming process may be
strongly modified by climate
warming , particularly at higher
latitudes.
Behrenfeld. 2014. Nature Climate Change. 4:880-892.
Green- bloom; Blue: Relative change in division rates
Changes in phytoplankton communities
• The timing and magnitude of seasonal blooms
are shifting in response to climate changes
(Edwards and Richardson. 2004. Nature 430:881-884)
• Dinoflagellates (eutrophic regions) and
flagellates (oligotrophic regions) are favored
under reduced mixing conditions and diatoms
under stronger mixing
Changes in phytoplankton communities
• Cyanobacteria have a competitive advantage
over other taxa in warmer, eutrophic
conditions. They have higher µmax than diatoms
and green algae at T above 25ᵒ. (Jöhnk at al. 2008. Global
Change Biol. 14:412-495)
• There are increases in harmful algal blooms
under warmer, eutrophic conditions. (EPA 820-S-13001)
Changes in phytoplankton communities
• Under reduced mixing conditions small cells have
high S/V, lower sinking rates and higher growth
rates (Litchman et al. 2007 Ecol. Letters 10:1170-1181)
• A shift to small-sized cells will result in lower
export which has positive feedbacks on the
climate system. Blooms of cyanobacteria and
dinoflagellates have large ecosystem impacts on
trophic transfer, water quality and fish
production
Changes in phytoplankton communities
• On geological times scales, marine diatom size
structure and diversity shifted toward smaller size
under warming temperature conditions (Finkel et al. 2005.
PNAS doi: 10.1073/PNAS.0709381104).
• In high latitude lakes, there has been an expansion
of pelagic, small diatom species in recent decades
probably due to a longer ice-free season and
increased stratification. (Smol et al. 2005. PNAS 102:4397-4402;
Rühland et al. 2008. Global Change Biol. 14: doi: 10.1111/j.1365-2486.2006.01670)
Cooler temperatures
Warmer Temperatures
(Smol 1983, 1988)
Warmer,
less ice
Colder,
extensive ice
Douglas and Smol (2010)
Hudson Bay area has recently undergone a climate regime
shift in the 1990s (Rühland et al. 2013, Proc Roy Soc Lond B)
Churchill Temperature Record: identifying thresholds
Δ -0.05°C
Δ +3.2°C
1991
-3
Mean Annual Temperature (ºC)
Breakpoint at 1991: p<0.0001
-4
-5
-6
-7
-8
-9
LOESS smoother (Span = 0.2)
-10
2010
2005
2000
1995
1990
1985
1980
1975
1970
1965
1960
1955
1950
1945
1940
Climate tipping point: diatoms respond
NORTH RAFT
12
-4
P<0.01. df=28
-5
10
8
-6
6
Diatoms (%)
-7
4
2
-8
0
-3
SPRUCE
6
-4
P<0.01, df=34
-5
4
-6
2
-7
0
-8
2005
2010
2015
1985
1990
1995
2000
1975
1980
1965
1970
1950
1955
1960
-4
1945
Fragilaria tenera (%)
Temperature (C)
Annual Temperature (°C)
Cyclotella taxa (%)
14
Rühland et al. 2013.
Proc. Roy. Soc. Lond. B
Lake of the Woods, Canada and USA - temperature
Whitefish Bay – Reference site
Annual Temperature
Cyclotella spp
Aulacoseira spp
4.5
50
4.0
40
30
3.0
20
2.5
10
2.0
1.5
R = 0.73
0
1.0
1900 1920 1940 1960 1980 2000 2020
4.5
60
4.0
50
3.5
3.0
40
2.5
30
2.0
20
1.5
R = - 0.65
1.0
10
1900 1920 1940 1960 1980 2000 2020
Rühland, Paterson, Smol 2008: Global Change Biology
Year AD
Relative Abundance (%)
Annual Temperature (ºC)
3.5
Phytoplankton declining in the oceans
There are consistent long-term trends since 1899 of
phytoplankton abundance (measured by chl) (Boyce et al. 2010).
sea surface temperatures (SST) were associated with
declining chl in 8 of 10 ocean basins.
SST leads to shallower mixed layer depth (MLD) which
limits nutrient supply in stratified tropical regions, but can
benefit phytoplankton at high latitudes where growth is
constrained by light availability and deep mixing.
Regional climate variability induces variation around the longterm trends and coastal processes such as land runoff can
modify chl trends in nearshore waters.
Blue shading indicates 95% confidence intervals.
Boyce et al. 2010. Nature 446:591-596.
Is there a decline in marine phytoplankton?
McQuatters-Gollop et al. (2011) argue that Boyce et
al. (2010) did not discuss contrary trends in
phytoplankton abundance seen by the Continuous
Plankton Recorder surveys in the North Atlantic over
8 decades (over 250,000 samples) and several other
long-term observations in other ocean basins. They
argue that Boyce et al. (2010) used correlations
between secchi depth and chl which may be highly
variable and which affect the trends in the early
years of the record and that they also restricted data
to the top 20m which does not take into account the
high levels of chl found in the deep chlorophyll
maximum. McQuatters-Gollop et al. argue that chl is
actually increasing in the North Atlantic, especially
since 1980.
McQuatters-Gollop et al. 2011. Nature 472: E6-E7. doi:10.1038/nature09950
Ocean Acidification
• Oceans have absorbed ca. one-third
of the CO2 produced by human
activities which has acidified surface
layers of the ocean (decrease of 0.02
pH units per decade over last 30 yrs
and 0.1 pH units overall).
• Resulted in substantial in
carbonate ions that is
unprecedented for millions of years.
Johnson et al. (2014), Contrasting effects of
ocean acidification on tropical fleshy and
calcareous algae. PeerJ 2:e411;DOI
10.7717/peerj.411
A study of the effects of
increasing CO2 and
resulting ocean acidification on
benthic algae on Palmyra Atoll
examined the tradeoffs
between enhanced
photosynthesis and impaired
biomineralization. Response
varied by species, but the
direction of response was
consistent within groups.
Brown: fleshy; Green: erect calcareous; Red: crustose
Johnson et al. (2014) PeerJ 2:e411;DOI 10.7717/peerj.411
Growth was enhanced in fleshy
macroalgae, calcification
was decreased in erect calcareous
algae, and net dissolution
occurred in crustose coralline
algae. There was no consistent
effect on algal photophysiology.
Results point to relative
abundance of fleshy macroalgae
on reefs and biomass of
calcifying algae with ocean
acidification.
Crustose Coralline Algae
• CCA are important marine calcifiers, especially on coral reefs
• CCA consolidate the reef platform and induce settlement of larvae
• CCA create habitats and promote biodiversity
• CCA are important in biogeochemical cycling, especially carbon
sequestration
• CCA are particularly sensitive to acidification because they have
high-magnesium calcite which is sensitive to dissolution
• Net calcification, growth and primary production have all been
shown to under CO2 concentrations.
Ordonez et al. 2014 Biol. Bull. 226:255-268.
• CCA cover showed a response to
increasing ρCO2 levels.
• The density of individuals for some CCA
taxa significantly with increased CO2.
• The number of reproductive individuals
of Pneophyllum sp. by 80% between
control and high CO2 levels.
• Effects on size structure of populations
was variable and species specific.
Ordonez et al. 2014 Biol. Bull. 226:255-268.
• Thick-crusted taxa had slower growth than
thin-crusted taxa.
• Changes is species composition of the CCA
community may be because of space
competition, variability in spore generation,
variability in settlement success, and effects
of increased CO2 on physiology.
•
of acidification in the future could lead to
species shifts from thick- to thin-crusted
species which may make them unable to
cement reefs enough to withstand high
disturbance events.
Ordonez et al. 2014 Biol. Bull. 226:255-268.
Coccolithophore calcification
• Emiliana huxleyi increases calcification and net primary production
under increased CO2. There has been a 40% increase in coccolith mass
over the past 220 years (Iglesias-Rodriguez et al. 2008. Science 320:336-340)
• E. huxleyi is expanding its range into the polar oceans and appears to be
more sensitive to temperature and salinity than to carbonate chemistry
(Winter et al. 2014. J. Plank Res. 36: 316-325)
• There was a progressive decrease in coccolithophore cell abundance and
diversity along a natural calcite saturation gradient caused by CO2 seeps
(Ziveri et al. 2014. Biol Bull. 226:282-290)
• Coccolithophores are important indicators of environmental conditions
and their physiology and ecology deserve more study.
Kübler and Dudgeon (2015) modeled the rates of photosynthesis in response to ρCO2,
temperature and their interaction under limiting and saturating photon flux densities
for red algae lacking carbon-concentrating mechanisms using published data.
Kübler and Dudgeon. 2015. PLoS ONE 10(7): e0132896. doi: 10.1371/journal.pone.0132806.
Major conclusions of the study:
Kübler and Dudgeon. 2015. PLoS ONE 10(7): e0132896. doi: 10.1371/journal.pone.0132806.
Effects of Climate Change on Global
Seaweed Communities
• Adaptation, migration, reshuffling of communities,
changes in herbivores.
• Seaweeds lacking CCMs are more likely to be C-limited
and thus more likely to benefit from increased CO2. Noncalcifying seaweeds as a group will likely respond
positively to increased CO2.
• Impacts on various life history stages are not well known,
but increasing T has been linked to mortality of spores,
gametophytes, eggs and sporophytes in Macrocystis
pyrifera.
• Some tropical species appear to have a limited scope for
acclimation compared to temperate counterparts,
presumably due to reduced environmental variability.
Harley et al. 2012. J. Phycol. 48:1064-1078.
Effects of Climate Change on Global
Seaweed Communities
• Ecosystem responses- changes in productivity, diversity,
resilience.
• Population declines and even local extinctions have been
documented at the warm end of species’ biogeographic ranges
during warming.
• Herbivores are key structuring agents in algal communities.
Elevated temperatures may reduce herbivore defenses in algae
and elevated CO2 may increase C:N and reduce palatability.
• Temperature may increase some herbivores, but heavily
calcified ones (eg. sea urchins) may be decreased by ocean
acidification.
• Warming may make seaweeds more susceptible to bacterial
disease.
Harley et al. 2012. J. Phycol. 48:1064-1078.
Coral Reefs
• Coral reefs face challenges from temperatures and ocean
acidification that are likely to lead to steep declines even by midcentury (Hoegh-Goldberg et al. 2007. Science 319:1737-1742; Baird and Maynard.
2008 Science 320: 315).
• Coral symbionts are key to understanding the potential for such
declines. Coral susceptibility to thermal bleaching- the heatinduced breakdown of their symbiosis with the dinoflagellate
Symbiodinium- is dependent on different types within that genus
which confer different levels of heat tolerance.
• Changes in symbiont composition (symbiont shuffling) depends
on the disturbance severity and the recovery environment (Cunning
et al. 2015. Proc. R. Soc. B. 282:20141725).
Corals and Their Symbionts
• Coral bleaching occurs when there
is a breakdown of the symbiosis
between cnidarian hosts and the
resident Symbiodinium spp.
Multiple mechanisms have been
proposed.
• Host cell apoptosis can contribute
to cell death of symbionts without
prior signaling from stressed or
dying symbionts, similar to an
immune response (Paxton et al. 2013. J.
Exp. Biol. 216: 2813-1820).
In experiments on the coral Orbicula faveolata
under experimental bleaching conditions, the
proportion of heat tolerant symbionts
dramatically following severe bleaching,
especially in a warmer recovery environment, but
tended to decrease if bleaching was less severe.
While the higher proportion of heat-tolerant
symbionts bleaching resistance, the
photochemical efficiency , suggesting that any
change in community structure oppositely impacts
performance and stress tolerance.
Even minor symbiont shuffling can adaptively
benefit corals, but fitness effects of the resulting
tradeoffs are hard to predict.
(Cunning et al. 2015. Proc. R. Soc. B. 282:20141725)
Corals and Their Symbionts
•
T in corals compromises photosynthesis by the symbionts,
leading to an production of reactive oxygen species which
causes a dissociation of the symbiont and host bleaching or death.
• Symbionts can exert significant control of host pH. The
photosynthetic activity of the symbionts plays a key role in
regulating the cellular response of their host to external CO2driven acidification.
• The number of Symbiodinium cells that a coral host contains may
influence the cellular response of the host to acidification and its
ability to calcify. (Gibbin et al. 2014. J. Exp. Biol. 217:1963-1069)
Large Benthic Foraminifera (LBFs)
• Tropical LBFs contain algal symbionts: diatoms, dinoflagellates,
rhodophytes. A general trend overall on holobiont growth was observed
across most LBFs in response to T and pH. The only exception was a
species that had a diatom symbiont. (Doo et al. 2014. Biol. Bull. 226:169-186)
• Porcelaneous taxa calcification under lower pH conditions and are not
nutritionally dependent on their dinoflagellate symbionts. Calcification of
hyaline taxa may be by ocean acidification conditions because they are
dependent on their diatom symbiont photosynthesis. There is a
porcelaneous LBF, Alveolinella, that harbors diatom symbionts which
deserves study. (Doo et al. 2014. Biol. Bull. 226:169-186)
• The majority of LBF species exhibited health in response to T.
• LBFs contribute ca 5% to reef-scale carbonate budgets, especially on
reef flats (Langer 2008. PLoS ONE 8: e54443)
Acidification Impacts in the Southern Ocean
• Strong evidence that light intensities strongly modify the effects of
acidification on phytoplankton.
• Chaetoceros debilis was grown at 390 and 1000 µatm ρCO2 under constant or
dynamic light condition.
• Dynamic light growth and strongly altered the effects of acidification on
primary production, being significantly under dynamic light at elevated
ρCO2.
• There were changes in cellular energy balance: energy transfer efficiency
from photochemistry to biomass production was drastically under
dynamic light at ρCO2.
• Because diatoms are major players in exporting C to depth, in their
abundance has biogeochemical significance.
Hoppe et al. 2015. New Phytologist 207:159-171
What can an Alga Do?
• Acclimate (metabolic changes)
• Adapt (genetic changes)
• Migrate
• Change symbiotic associations
• Reshuffle communities
• Change responses to loss processes (sinking,
herbivores, cell death)
Why should we care?
• Algae produce oxygen- about half of the total every year.
• Algae are at the base of the food web in aquatic ecosystems.
They may be declining and changes in community structure can
affect food webs
• Algae are important symbionts in many organisms, especially
those associated with coral reefs
• Algae can form harmful algal blooms and warming climates
increase frequency and duration of blooms
• Algae form increasing ‘dead zones’ in coastal environments
• Algae are just plain interesting!
It’s the only planet we have
Let’s take care of it!
Thank you for your attention